Tuesday, November 15, 2011

Visual hallucinations and the Visual Cortex

Thanks to a helpful tip I was able to find a very interesting article all about what hallucinations come from in the brain.  The article titled What Geometric Visual Hallucinations Tell Us about the Visual Cortex. Neural Computation by Bressloff, Cowan, Golubitsky, Thomas and Wiener (http://www.math.utah.edu/~bresslof/publications/01-3.pdf) is extremely useful information on where hallucinations originate within the brain.  Bressloff states that images are generally seen in both eyes and move with them, but maintain their relative positions in the visual field.  This leads him to believe that the above statement is evidence enforcing that hallucinations are generated in the brain.  Sited in the article is information stating that when subjects are instructed to inspect the fine details of their hallucination the fMRI of the V1 area of the brain shows increased activity.  Is it possible that it is coincidence, and does the fMRI show increased activity in areas of the brain responsible for creativity? Is there a possibility that connections between these areas of the brain are linked with areas of the brain responsible for rationalizing thoughts?  Could an error in communication between these areas be responsible for manifesting hallucinations?

What Geometric Visual Hallucinations Tell Us about the Visual Cortex answers this question by with this quote “a nonuniform retino-cortical magnification is generated by the nonuniform packing density of ganglion cells in the retina, whose axons in the optic nerve target neurons in the lateral geniculate nucleus (LGN), and in V1, that are much more uniformly packed.  The article then goes on to prove with using mathematics (which are way over my head) reinforcing that constants are generated in V1.  In addition, this article also gives significant evidence to suggest that iso-orientated patches located on a hypercolumn are the circuits in V1 responsible for detection of oriented edges and formation of contours commonly seen in hallucinations.  This is further evidence suggesting that the V1 area of the brain should in fact show higher levels of activity using fMRI when subjects reporting hallucinations are asked to describe the fine details of their hallucinations.

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